Effects of IL-1beta on gene expression in human rheumatoid synovial fibroblasts

IL-1 is one of the key mediators involved in the pathogenesis of rheumatoid arthritis (RA) and is known to affect the level of gene expression in various settings. We investigated the effects of IL-1beta on the expression of 240 genes in rheumatoid synovial fibroblasts (RSFs) using a cDNA microarray. Total RNAs were prepared from RSFs stimulated with IL-1beta and hybridized to the microarray. The fluorescence intensity of each gene was compared between the control and IL-1beta-treated cells. To confirm the data obtained from the microarray analysis, the level of gene expression was also examined by ELISA, Northern blot, or Western blot depending on the genes to be analyzed. The genes whose levels were significantly changed by IL-1beta in the microarray analysis could be divided into three categories; inflammatory mediators, matrix-modifying enzymes, and apoptosis-associated molecules. The increase in the mRNA levels of IL-6, IL-8, MCP-1, and GRO-1 was confirmed by determining their protein levels from the cell culture supernatant using ELISA. The increase in the level of two matrix-degrading enzymes, MMP-1 and MMP-3, was reproducibly observed by an ELISA method, while the decrease in the level of TIMP-3, an inhibitor of MMPs, was confirmed by Northern blot analysis. The fluorescence intensity of two apoptosis-related genes, caspase-3 and Bcl-xL, was significantly lowered. The decreased protein level of caspase-3 was also found. Our data suggested that IL-1beta could provoke a series of responses in RSFs leading to the pathologic status of RA, including enhancement of inflammatory cytokines, imbalanced production of MMPs and TIMPs, and dysregulation of apoptosis.